The present invention relates to a solid-state image pickup device capable of high-speed transfer of signal charges in a horizontal direction and, more specifically, to a CCD (charge-coupled device) for use in an electronic still (digital still) camera and a PC (personal computer) camera which adopts a progressive scanning system.
A solid-state image pickup device, which has recently been used a lot, has the advantages that it is smaller, lighter and longer in lifetime than an image pickup tube. In particular, an interline transfer CCD (hereinafter referred to as IT-CCD) is used widely in a video camera for household use, a hand-held camera for broadcast use, etc. A digital still camera employs a CCD of a progressive scanning system capable of outputting signals of all pixels independently. This CCD needs to decrease in smear when no mechanical shutter is used and to increase the area of a chip corresponding to a film. In other words, the number of transfer stages of vertical transfer sections has to be made twice as large as that of a conventional CCD in order to realize the progressive scanning type CCD. For example, in a progressive scanning type IT-CCD, the existent two-layer-electrode/four-phase-driving can be changed to a three-layer electrode/three-phase driving in order to double the number of transfer stages of the vertical transfer sections. In this case, however, the structure of the CCD is complicated. Moreover, the number of transfer stages can be doubled by forming a wire so as to cross the center of light-receiving sections and two-layer-electrode/four-phase-drive the CCD; however, in this case, the sensitivity of the CCD is lowered.
In contrast, a frame transfer CCD (hereinafter referred to as FT-CCD) allows progressive scanning to be easily obtained by two-layer-electrode/four-phase-driving. However, an influence of smear becomes serious without using any mechanical shutter.
Furthermore, in the IT-CCD and FT-CCD, if the area of a chip or the number of pixels is increased, the capacity of transfer electrodes is increased and so is the power consumption of driving circuits.